This invention relates to tunnel ovens.
One known form of tunnel oven has its baking chamber divided by partition means into a plurality of longitudinally extending zones, through which an oven conveyor passes in the form of an endless steel mesh band, openings being provided in the partitions to permit the oven band to pass from one zone to the next.
In considering a tunnel oven applied to the baking of biscuits, cereals etc., the length of the oven chamber may be 60 meters divided up into five interconnected zones each 12 meters long. Due to the nature of the product being baked, it is sometimes necessary to maintain the temperature at different levels along the length of the oven, for instance 300.degree. C. in the first zone and 200.degree. C. in the last zone.
Tunnel ovens may be of the direct fired type and employ a plurality of lateral strip burners or distributed hot air heated from a single zonal burner source. Alternatively, the oven may be of the indirect fired type employing, for example, a zonal heat exchanger which transmits heat by radiation or convection.
In tunnel ovens a suction fan may be employed to remove the steam produced from baking. However, air, or oven atmosphere, is also removed along with combustion gases (if a direct fired oven) at the same time. Air or atmosphere so removed is naturally replaced by air flowing into the oven from the feed and discharge ends thereof.
It has been found that this inflowing air may have a bad effect on the baking of the articles due to the comparatively cold indrawn air upsetting the temperature conditions within the baking chamber.